1. Field of the Invention
The present invention relates to a nonvolatile semiconductor memory device.
2. Description of the Related Art
In recent years, multilevel technology, in which a plurality of threshold value states are assigned to one memory cell to enable storage of multiple bits of information in the memory cell, has become standard as a way of realizing increased capacity in nonvolatile memory.
However, this multilevel technology results in a reduction in the gap between threshold distributions used to express data. Consequently, misreading of a memory cell resulting from the threshold distribution of the memory cell being mistakenly written to a different position to the desired position due to, for example, malfunction of the memory cell or application of an excessive write voltage, occurs more easily.
To deal with this problem, there is a nonvolatile memory provided with an error detection and correction function using ECC (Error Correcting Code) aimed at improving reliability of data. Such nonvolatile memory requires generation of redundant ECC data based on data supplied by the host, and configuration of an ECC frame. This results in the problem of an increased burden of system processing, whereby system performance cannot be fully displayed.